U.S. patent application number 11/888521 was filed with the patent office on 2009-02-05 for expansion valve control system and method for air conditioning apparatus.
This patent application is currently assigned to American Standard International, Inc.. Invention is credited to Jonathan David Douglas.
Application Number | 20090031740 11/888521 |
Document ID | / |
Family ID | 40336846 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090031740 |
Kind Code |
A1 |
Douglas; Jonathan David |
February 5, 2009 |
Expansion valve control system and method for air conditioning
apparatus
Abstract
A vapor compression air conditioning system includes a motor
operated expansion valve and control unit including sensors for
determining the amount of superheat of the working fluid at or
adjacent to the compressor inlet. Expansion valve position is
adjusted to maintain a predetermined amount of superheat. The
sensors may sense working fluid evaporator temperature and
temperature downstream of the evaporator. Dual motor operated
expansion valves may be disposed in the working fluid conduit
between the heat exchangers in a reversible system. In operation,
the expansion valve position may be set as a function of ambient
temperature, a previous position, and predetermined superheat
requirements to minimize liquid ingestion by the compressor.
Inventors: |
Douglas; Jonathan David;
(Bullard, TX) |
Correspondence
Address: |
WILLIAM J. BERES;THE TRANE COMPANY
PATENT DEPARTMENT - 12-1, 3600 PAMMEL CREEK ROAD
LA CROSSE
WI
54601
US
|
Assignee: |
American Standard International,
Inc.
NEW YORK
NY
|
Family ID: |
40336846 |
Appl. No.: |
11/888521 |
Filed: |
August 1, 2007 |
Current U.S.
Class: |
62/225 ;
236/92B |
Current CPC
Class: |
F25B 41/31 20210101;
F25B 13/00 20130101; F25B 2500/28 20130101; F25B 2313/005 20130101;
F25B 2600/01 20130101; F25B 2700/2106 20130101; F25B 2700/1933
20130101; F25B 2700/2117 20130101; F25B 2500/26 20130101; F25B
2700/21151 20130101; Y02B 30/70 20130101; F25B 41/34 20210101; F25B
2500/27 20130101; F25B 2600/21 20130101 |
Class at
Publication: |
62/225 ;
236/92.B |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 41/06 20060101 F25B041/06 |
Claims
1. In a vapor compression air conditioning system including a
compressor, and a fluid circulating circuit including a condenser
heat exchanger and an evaporator heat exchanger interconnected by a
first fluid conducting conduit, the improvement comprising: a motor
operated expansion valve interposed in said first conduit between
said condenser heat exchanger and said evaporator heat exchanger;
at least one sensor for measuring a parameter related to a
condition of a working fluid flowing through a second conduit
between said evaporator heat exchanger and an inlet to said
compressor; and a control unit operably connected to said expansion
valve and said at least one sensor for setting a position of said
expansion valve in a first operating mode of said system to control
the flow of working fluid through said evaporator heat exchanger to
maintain a predetermined amount of superheat of said working fluid
in said second conduit.
2. The system set forth in claim 1 wherein: at least two sensors
are provided for measuring parameters related to the condition of
said working fluid in said second conduit, said at least two
sensors comprising a temperature sensor and a pressure sensor.
3. The system set forth in claim 2 including: an ambient outdoor
temperature sensor operably connected to said control unit.
4. The system set forth in claim 2 wherein: at least two
temperature sensors are provided for measuring the working fluid
temperature at an inlet to said evaporator heat exchanger and at an
outlet of said evaporator heat exchanger, said temperature sensors
being operably connected to said control unit.
5. The system set forth in claim 1 wherein: said system includes a
working fluid flow reversing valve for converting said condenser
heat exchanger to an evaporator heat exchanger and said evaporator
heat exchanger to a condenser heat exchanger and said control unit
is operable to cause said motor operated valve to operate in a
position to provide substantially unrestricted flow of fluid
between said heat exchangers.
6. The system set forth in claim 1 including: a reversing valve for
reversing the flow of working fluid between said compressor and
said condenser heat exchanger and between said compressor and said
evaporator heat exchanger and a second expansion valve disposed in
said first conduit between said condenser heat exchanger and said
evaporator heat exchanger for controlling the flow of working fluid
through said system when said system is operated in a second
operating mode.
7. The system set forth in claim 6 wherein: said second expansion
valve is motor operated and is operably controlled by said control
unit.
8. The system set forth in claim 6 wherein: said second expansion
valve is a thermal type expansion valve.
9. The system set forth in claim 1 wherein: said motor operated
expansion valve is disposed in a component of said system disposed
outdoors.
10. The system set forth in claim 1 wherein: said motor operated
expansion valve is disposed in a component of said system disposed
indoors.
11. The system set forth in claim 1 wherein: said control unit
comprises an electrical control circuit connected to signal input
conductor means for receiving a signal related to at least one of
operation of said system to energize said compressor, a position of
a working fluid circuit reversing valve and a signal from said at
least one sensor.
12. The system set forth in claim 11 wherein: said control unit
includes means for inputting values to said control circuit related
to at least one of the type of working fluid, the capacity of said
compressor, an operating mode of said system, and a relationship
between the amount of superheat of said working fluid and a change
in evaporator temperature to achieve a predetermined amount of
superheat.
13. The system set forth in claim 12 wherein: said values in said
control circuit related to said relationship between the amount of
superheat and said evaporator temperature comprises a constant
value of change in evaporator temperature.
14. In a vapor compression air conditioning system including a
compressor and a fluid circulating circuit including a condenser
heat exchanger and an evaporator heat exchanger interconnected by
fluid conducting conduits, said system including a motor operated
expansion valve interposed in a conduit between said condenser heat
exchanger and said evaporator heat exchanger, at least one sensor
for measuring a parameter related to a condition of a working fluid
flowing between said evaporator heat exchanger and an inlet to said
compressor, and a control unit operably connected to said expansion
valve and said at least one sensor, a method of controlling the
position of said expansion valve comprising the steps of: in a
first operating mode of said system controlling the flow of working
fluid through said evaporator heat exchanger to maintain a
predetermined amount of superheat of said working fluid flowing to
said compressor inlet.
15. The method set forth in claim 14 including the step of: causing
said control unit to respond to a signal for energizing said system
to move said expansion valve to a position based on the outdoor
ambient temperature.
16. The method set forth in claim 15 including the step of: varying
the gain of said control unit as a function of a current position
of said expansion valve.
17. The method set forth in claim 15 including the step of: varying
the gain of said control unit as a function of measured
superheat.
18. The method set forth in claim 15 including the step of: moving
said expansion valve to an initial position based on an estimate of
the evaporating temperature and condensing temperature of said
working fluid and wherein said condensing temperature is based on
said outdoor ambient temperature.
19. The method set forth in claim 14 including the step of: causing
said control unit to respond to a signal for energizing said system
to move said expansion valve to a position based on at least one of
a previous position of said expansion valve and a position based on
an estimate of the operating temperature of said evaporator heat
exchanger.
20. The method set forth in claim 14 including the step of: causing
said control system to move said expansion valve to a predetermined
position dependent on elapsed time from a signal to start said
compressor.
21. The method set forth in claim 14 including the step of: prior
to startup of said system, moving said expansion valve to a
predetermined position which position is a fraction of a desired
valve position and then providing a signal to energize said
compressor.
22. The method set forth in claim 14 including the step of:
measuring superheat of said working fluid at said compressor inlet
during operation of said system and causing said expansion valve to
control flow of working fluid to maintain an evaporator heat
exchanger temperature which will provide a predetermined amount of
superheat of said working fluid at said compressor inlet.
23. The method set forth in claim 14 including the step of: causing
said control unit to close said expansion valve prior to
de-energizing said compressor.
24. The method set forth in claim 14 including the step of:
deenergizing said compressor when the evaporator temperature is a
predetermined number of degrees below the evaporator temperature
just prior to a signal to de-energize said compressor to minimize
ingestion of liquid working fluid by said compressor on a
succeeding startup thereof.
25. The method set forth in claim 14 including the step of:
providing a signal to said expansion valve to move to a position to
minimize restriction of working fluid flow directly from said
evaporator heat exchanger to said condenser heat exchanger.
26. The method set forth in claim 14 including the step of:
de-energizing said compressor in response to sensing a
predetermined condition of superheat of said working fluid for a
predetermined period of time.
27. The method set forth in claim 14 including the step of:
de-energizing said compressor in response to operation of said
system at a predetermined low pressure of said working fluid at
said compressor inlet for a predetermined period of time.
28. The method set forth in claim 14 including the step of:
adjusting the position of said expansion valve based on a history
of positions of said expansion valve over a predetermined period of
time.
Description
BACKGROUND OF THE INVENTION
[0001] In the art of vapor compression type heating, ventilating
and air conditioning (HVAC) equipment, there has been a continuing
need to provide a suitable expansion device which may be reliably
controlled to minimize the chance of damage to the system
compressor resulting from liquid working fluid entering the
compressor, maintain the ability during steady state operation to
adjust working fluid flow to meet system requirements and to
otherwise protect the compressor from damage during system shutdown
or during periods of continuous low compressor suction pressure or
a low super-heat condition of the working fluid.
[0002] Although prior efforts have been made to provide so-called
motorized or power operated expansion valve devices in commercial
sizes of air conditioning equipment, such devices and associated
controls have not been economically practical, reliable in
operation, nor able to provide suitable control over refrigerant
fluid flow to control superheat at the compressor inlet for lower
capacity (1 to 5 ton) configurations of vapor compression type air
conditioning equipment. It is to overcome these deficiencies
associated with prior art systems and methods that the present
invention has been developed.
SUMMARY OF THE INVENTION
[0003] The present invention provides an improved air conditioning
apparatus or system including an electronic control system for
controlling the refrigerant working fluid expansion valve to
control fluid superheat prior to introducing the fluid to the
system compressor. The present invention also provides an improved
method of controlling working fluid flow in a vapor compression
type air conditioning system to minimize the chance of damage to
the system compressor during certain phases of operation.
[0004] In accordance with one aspect of the present invention, a
vapor compression type air conditioning system is provided with a
motor controlled expansion valve which is responsive to a
controller which includes temperature and/or pressure sensors
suitably positioned on the apparatus for controlling refrigerant or
working fluid flow. Refrigerant or so-called working fluid flow is
controlled such that working fluid in the liquid phase will not
likely enter the system compressor by providing for a predetermined
amount of superheat of the fluid at or upstream of the compressor
inlet port. The expansion valve controller or control system
includes a control circuit operably connected to an electric
stepper motor type expansion valve. The control circuit is also in
communication with plural temperature sensors or a combination of
temperature and pressure sensors for measuring working fluid
condition during operation of the system. The temperature sensors
may comprise a so-called outdoor temperature sensor, a temperature
sensor for sensing the temperature of the working fluid downstream
of the evaporator or evaporating heat exchanger and upstream of the
compressor inlet port or a combination of temperature sensors,
together with a sensor which determines the status of the
compressor (on or off).
[0005] The present invention also provides a control system for a
vapor compression type air conditioning apparatus or system for
controlling working fluid superheat according to a preferred
control algorithm or method which provides for valve control during
system startup, steady state operation and system shutdown. On
system startup, for example, a method in accordance with the
invention provides a predetermined position of the expansion valve
and a predetermined delay in startup of the system compressor or
compressors.
[0006] A method in accordance with the invention provides, during
steady state operation, for an estimate of future changes in
evaporator temperature based on historical changes in expansion
valve position, and adjustments to valve position are made based on
a novel procedure. Still further, the invention contemplates the
provision of an improved system shutdown procedure wherein the
expansion valve is closed prior to compressor shutdown and the
compressor is de-energized at a predetermined change in evaporator
temperature to reduce the chance of liquid ingestion into the
compressor during a following starting cycle.
[0007] Still further, the invention provides for compressor
protection in accordance with procedures which monitor fluid inlet
conditions at the compressor to protect the compressor against
failures of the expansion valve and other major components, such as
fan motors, and improper refrigerant fluid charge level.
[0008] Those skilled in the art will further appreciate the
abovementioned advantages and features of the invention together
with other important aspects thereof upon reading the detailed
description which follows in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic diagram of one preferred embodiment of
an air conditioning apparatus or system including an expansion
valve and control system in accordance with the invention;
[0010] FIG. 2 is a schematic diagram similar in some respects to
the diagram of FIG. 1 and illustrating a first alternate embodiment
of the invention;
[0011] FIG. 3 is a schematic diagram similar to FIGS. 1 and 2 and
illustrating a second alternate embodiment of the invention;
[0012] FIG. 4 is a detailed schematic diagram showing a preferred
location of temperature sensors in relation to a heat exchanger or
so-called evaporator apparatus comprising part of a system of the
present invention;
[0013] FIG. 5 is a generalized flow diagram in accordance with one
method of the invention;
[0014] FIG. 6 is a generalized flow diagram also in accordance with
one method of the invention;
[0015] FIG. 7 is a table illustrating certain features in
connection with another method of the invention;
[0016] FIG. 8 is a block diagram of an expansion valve controller
illustrating respective input and output signal paths; and
[0017] FIG. 9 is a diagram showing change in evaporator temperature
required to achieve predetermined superheat of the working
fluid.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In the description which follows like elements are marked
throughout the specification and drawings with the same reference
numerals, respectively. The drawing figures may be shown in
somewhat generalized schematic form in the interest of clarity and
conciseness.
[0019] Referring to FIG. 1, there is illustrated a schematic
diagram of an air conditioning apparatus or system, generally
designated by the numeral 10. Apparatus 10 may be configured as a
so-called heat pump or a reversible air conditioning apparatus
which is operable to provide both cooling of an enclosed space and
heating of the space. In the configuration of the apparatus or
system 10, it is operating as a so-called air conditioner or in a
cooling mode, and includes a so-called indoor unit 11a in
communication with an enclosed space, not shown, for which air is
circulated by a motor driven fan, also not shown, and in contact
with an indoor heat exchanger or indoor coil 12.
[0020] The apparatus 10 also includes an outdoor unit 11b including
a heat exchanger or so-called outdoor coil 14. Heat exchangers 12
and 14 are interconnected by a conduit 16, including a refrigerant
fluid bidirectional filter and dryer apparatus 18 of a suitable
type. Heat exchangers 12 and 14 are also operably connected to a
so-called switchover or reversing valve 20 by way of conduits 22
and 24. Switchover valve 20 is also operably connected to a
compressor 26. Compressor 26 is connected to a refrigerant or
working fluid conduit 30 at an inlet port 26a. Compressor 26 is
also connected to a conduit 32 for discharging heated, pressure gas
thereto, via a port 26b. Those skilled in the art will recognize
that the system 10 as well as other systems described herein may
include a single compressor such as compressor 26 or two or more
compressors or one or more variable capacity compressors or
combinations thereof. Conventional controls for operating the
compressor 26, including a so-called thermostat, are not
illustrated in FIG. 1. However, FIG. 1 does illustrate a control
unit, generally designated by the numeral 34, for controlling an
electronic motorized expansion valve 36. Expansion valve 36 is
interposed heat exchangers 12 and 14 in conduit 16 for controlling
fluid flowing from heat exchanger 14 to the heat exchanger 12. The
direction of fluid flow in the apparatus 10, in the position of
valve 20, as indicated, is in accordance with the arrows 10a and
10b in FIG. 1. Expansion valve 36 may be disposed in indoor unit
11a, as shown, or interposed in conduit 16 in outdoor unit 11b.
Still further, the indoor and outdoor units 11a and 11b may be
combined in one cabinet as a so-called package unit known to those
skilled in the art. Control unit 34 is also operably in
communication with an outdoor temperature sensor 38 and respective
pressure and temperature sensors 40a and 40b. Sensors 40a and 40b
are operable to measure the pressure and temperature of the working
fluid flowing through conduit 30 to the compressor inlet 26a.
[0021] The control unit 34 includes a programmable microprocessor
which will be explained in further detail hereinbelow. Basically,
the control unit 34 will interface with the standard controls for
the apparatus 10 for controlling the operation of the valve 36 so
that a suitable amount of superheat condition of the working fluid
exists as the fluid leaves the heat exchanger or evaporator 12 and
flows through conduits 24 and 30 so as to prevent or minimize the
flow of liquid working fluid through these conduits and which may
be ingested by the compressor 26. Moreover, control of the valve 36
may be carried out in other modes of operation to minimize the risk
of liquid ingestion into the compressor 26.
[0022] For example, at startup of the apparatus 10, control unit 34
may be operated to at least partially open valve 36 prior to
energization of the compressor 26. Moreover, at compressor startup
the valve 36 may also be controlled as to its fluid flow
controlling position as a function of the ambient outdoor
temperature, as determined by sensor 38. During steady state
operation, the valve 36 may be continuously adjusted based on a
weighted history of recent valve positions and also based on the
working fluid temperature and pressure sensed by the sensors 40a
and 40b, so as to maintain the requisite amount of superheat of the
fluid flowing to the compressor inlet. Still further, the apparatus
10 may be shutdown, that is the compressor motor de-energized, in
response to defined periods of continuous low fluid superheat and
defined periods of continuous low pressure in conduit 30 leading to
the compressor inlets.
[0023] One preferred mode of operation of the system or apparatus
10 may also be based on startup or initializing the position of
valve 36 by estimating the operating evaporator temperature and the
operating condensing temperature by adding a constant value to the
outdoor temperature sensed by the sensor 38. The estimated working
fluid evaporating temperature and condensing temperature are
applied to a so-called compressor map to obtain an estimate of the
refrigerant or working fluid mass flow and the starting position of
the valve 36 may be calculated using a mathematical model of the
expansion valve to find the valve position corresponding to the
calculated mass flow. Thus, the control unit 34 may begin to move
the valve 36 to its initial position and the compressor 26 is not
started until the valve has reached fifty percent of its initial
position, for example. Once an evaporator temperature has
stabilized, the control unit 34 enters a so-called steady state
mode of operation.
[0024] During steady state operation, a predetermined timeline
history of change in valve position may be maintained, such as
every three minutes. At predetermined intervals, such as every 2.5
seconds, history points are multiplied by a weighting array and
more recent points are weighted higher than points further in the
past so that the sum of the history points, multiplied by the
weighting array is an estimation of expected future changes in the
evaporator temperature. By way of example, adjustments to the valve
position (DStep) may be made using the following equation:
DStep=(ET.sub.goal-ET+future ET))/gain
[0025] The gain may be expressed as the change in the temperature
at the evaporator inlet, otherwise known as evaporator temperature
(ET), per valve step and is a function of valve position. Gain
versus valve position may be calculated by matching the refrigerant
or working fluid flow from the aforementioned compressor map to
that of the valve at various operating points. Gain may be
predetermined and stored in the control unit or controller in
tabular form as a function of valve position. It is significant to
note that the gain is only a function of valve position and is
independent of compressor size.
[0026] The "evaporator temperature goal" (ET.sub.goal) is based on
current superheat conditions. Using experimental data, a table may
be created listing the change in evaporator temperature (ET)
required to reach 10.degree. F. of superheat, for example.
[0027] On shutdown of the apparatus 10, the control unit 34 may be
operated to record the current evaporator temperature (ET) and
cause closure of valve 36 prior to shutting down the compressor 26.
In this way the compressor is turned off when the current
evaporator temperature is at least one degree below the evaporator
temperature prior to shutdown and a slight pump-down reduces the
chance of flooding of the compressor with liquid refrigerant fluid
on the next startup of the apparatus 10.
[0028] In the event of failure of the control unit 34 to maintain
superheat at a predetermined value, an additional process may
involve monitoring the fluid inlet conditions of the compressor 26
to protect the compressor against failure if the valve 36 should
fail to operate properly or other key components should fail to
operate properly, such as the condenser or evaporator fan motors,
or other apparatus, causing the flow of heat exchange fluid across
the heat exchangers 12 or 14, or there exists an insufficient
charge of working refrigerant fluid in the system or apparatus
10.
[0029] Since low working fluid superheat is an indication of liquid
returning to the compressor 26 via the conduit 30, such a condition
is continuously monitored with the sensors 40a and 40b and a
warning signal may be registered after a predetermined period of
continuous low superheat. For example, after a predetermined period
of continuous low superheat, the control unit 34 may send a signal
to the main control unit for the compressor 26 of system 10 for
executing a shutdown signal. Also, for example, low suction
pressure in conduit 30 indicates low refrigerant fluid mass flow
and low mass flow does not provide sufficient cooling which will
cause compressor damage due to overheating. In the heating mode of
operation in an apparatus, such as the apparatus 10, the evaporator
temperature (ET) varies with the outdoor ambient temperature and a
warning signal may be issued when the evaporator temperature, as
calculated from compressor suction pressure, is more than a
predetermined amount below the ambient outdoor temperature, such as
30.degree. F., for example.
[0030] Still further, faulty operation of other key components in
an apparatus or system, such as the apparatus 10, may be detected
using compressor suction pressure or temperature, as determined by
the sensors 40a and 40b, and the ambient temperature sensor 38 in
conjunction with the position of the valve 36. Since performing
diagnostics on a system, such as that illustrated in FIG. 1,
typically requires knowledge of the pressures in the conduit 30, as
well as conduit 32, the pressure in the conduit 32 can be estimated
based on the measured pressure in the conduit 30. System faults and
symptoms thereof may be tallied based on evaporator temperature,
the superheat condition, and the so-called high-side working fluid
pressure in conduit 32. For example, a failure of a motor driven
fan to blow sufficient air over the heat exchanger or condenser 14
results in high pressure in conduits 32 and 22 which can be
determined based on measuring the pressure in conduit 30 by sensor
40a. Failure of a motor driven fan to blow sufficient air over the
heat exchanger or evaporator coil of heat exchanger 12 results in a
low evaporator temperature. A low refrigerant fluid charge in
system 10 results in both a low evaporator temperature and a low
high-side pressure in conduits 22 and 32.
[0031] Still further, if a compressor is not pumping fluid
sufficiently, the evaporator temperature will become high and the
high-side working fluid pressure will, of course, become low. If
there is a liquid line restriction in conduit 16 or valve 36 is
stuck closed, the evaporator temperature will be low and the
superheat condition will be high, while the high-side pressure will
be normal. In the event of the valve 36 being stuck in a wide-open
or almost fully open condition, the evaporator temperature will be
normal, but the superheat condition, as determined from sensors 40a
and 40b, will be low while the high-side pressure in conduits 32
and 22 will be normal.
[0032] Another benefit of motor operated expansion valve 36 and a
control unit therefor, such as the control unit 34, is that valve
36 can be purposely controlled to be in the wide-open position,
thereby functioning as a check valve when the system 10 is running
with the working fluid flowing in the so-called opposite direction,
that is wherein the heat exchanger 12 acts as a condenser and the
heat exchanger 14 acts an evaporator. This condition of operation
is also, essentially known as the "heat pump" mode of operation or
"heating mode".
[0033] Referring now to FIG. 2, there is illustrated another
embodiment of a system or apparatus in accordance with the
invention and generally designated by the numeral 50. The apparatus
or system 50 also includes an indoor unit 51a and an outdoor unit
51b. Apparatus or system 50 also includes a compressor 26, heat
exchangers 12 and 14 connected to the compressor by way of a
reversing or switchover valve 20, and conduits 16, 24, 30, 32 and
22, as illustrated. Pressure and temperature sensors 40a and 40b
are operably associated with conduit 30 leading to compressor inlet
26a for measuring the pressure and temperature of the refrigerant
working fluid flowing therethrough. Sensors 40a and 40b are
operable to provide signals to a control unit 34a which is in
communication with motor controlled expansion valves 36a and 36b,
both interposed in conduit 16 and both operable to function as
check valves, as indicated by the symbols 36c. Control unit 34a may
communicate with valves 36a and 36b via one or more modes of
communication including hardwiring, radio frequency signal
transmission or optical signal transmission, for example. Apparatus
50 thus operates as a heat pump, which is the condition
illustrated, and enjoys all of the advantages of the apparatus 10.
When operating in a cooling mode, motor controlled expansion valve
36a is regulated to provide the requisite amount of superheat of
the fluid flowing through conduit 30 while expansion valve 36b is
held in a wide-open position to function as a so-called integrated
check valve, indicated by symbol 36c. Conversely, when the
apparatus 50 is operating as a heat pump, heat exchanger 12 is
rejecting heat to a suitable enclosed space and expansion valve 36a
is held in a wide-open position while expansion valve 36b is
controlled by control unit 34a to provide the requisite amount of
superheat for working fluid flowing from conduit 22 to reversing or
switchover valve 20 and then to conduit 30.
[0034] Referring now to FIG. 3, yet another preferred embodiment of
the invention is illustrated and generally designated by the
numeral 70. Apparatus or system 70 includes elements included in
the embodiments of FIGS. 1 and 2, as indicated by the corresponding
reference numerals. However, the system 70 is provided with two
temperature Sensors 41 and 43 which measure temperature at selected
locations with respect to and generally at the heat exchanger 12.
The embodiment of FIG. 3 also includes a thermal type expansion
valve 37 interposed in liquid line 16 and including a conventional
check valve 37c. Accordingly, the amount of superheat of the fluid
flowing through conduits 24, valve 20 and conduit 30 is determined
by measuring temperatures at sensors 41 and 43 instead of a
temperature and pressure measurement in conduit 30.
[0035] In the embodiment of FIG. 3, the so-called outdoor unit,
comprising the components illustrated within the envelope 71, is
provided with a thermal expansion valve for operation in the
heating mode, as indicated by the expansion valve 37, while motor
controlled expansion valve 36 is utilized on an indoor unit
comprising the components illustrated within envelope 73 and which
includes heat exchanger 12, and a control unit 34c, similar to
control units 34 and 34a.
[0036] Referring briefly to FIG. 4, there is illustrated a more
detailed configuration of the heat exchanger 12 and preferred
locations of temperature sensors 41 and 43 as well as expansion
valve 36. The location of sensor 43, which is typically in the
two-phase region of fluid flow into and through the heat exchanger
12, measures the so-called evaporator temperature (ET) and,
together with the sensor 41, enables the determination of the
amount of superheat of the fluid flowing to the compressor via the
conduits 24 and 30, for example. Other locations of the sensors 41
and 43 on the heat exchanger 12 may be suitable.
[0037] Referring to FIG. 5, there is illustrated a flow diagram of
major steps for startup of an apparatus or system in accordance
with one embodiment of the invention. As mentioned previously, upon
a "call" for cooling or heating by a thermostat controller not
shown, but associated with the control unit 34, 34a or 34c, as
indicated by step 90, the motor controlled expansion valve 36, 36a
or 36b would be open to the same position as the last position in a
previous operating cycle, as indicated at step 92. This step would
be followed by step 94 which is a timing step to wait until the
valve 36, 36a or 36b is moved to at least 50% of the desired open
position of the valve, which may take as long as twelve seconds for
suitable commercially available versions of the valve, as indicated
at step 94. Once the expansion valve 36, 36a or 36b has opened to
the 50% open position, the compressor 26 and/or 28 would be
started, as indicated at step 96, followed by a step 98 in which a
valve positioning profile would be that which might be predefined
and programmed in the controller 34, 34a or 34c. After following
the predefined valve movement profile for ninety seconds, for
example, as indicated by step 98, a feedback control mode would be
carried out at step 100 during steady state operation of the
associated system or apparatus.
[0038] As shown in FIG. 6, once a cooling or heating "call" has
been satisfied at a step 102, if the superheat condition of the
fluid flowing toward the compressor 26 and/or 28 was within a
so-called dead band of the setpoint of superheat, the current
position of valve 36, 36a, 36b would be stored in a memory of the
control unit 34, 34a or 34c, as indicated at step 104. Step 104
would be followed by a step 106 of closing the expansion valve 36,
36a or 36b followed by step 108 which would be a time of
approximately ten seconds, for example, followed by shutdown of
compressor 26 and/or 28 at step 110.
[0039] Referring now to FIG. 7, there is illustrated a table of
values of time in seconds, the position of the expansion valve 36,
36a or 36b as a percent open relative to the initial starting
position of the valve. The column entitled "weight" is a set of
values related to a fixed profile of valve position relative to a
feedback control signal. A weight of 100, for example, indicates
that one hundred percent of valve control will be due to a fixed
valve position profile. A weight of zero indicates that one hundred
percent of valve control will be due to a feedback signal from the
superheat control unit. Accordingly, the starting method of the
invention comprises, for example, a period beginning at compressor
startup and ending one hundred eighty seconds later. During such
period, the position of the expansion valve 36 is independent of
the temperature sensed at sensors 41 and 43 in FIG. 4, for example.
Accordingly, the control unit 34c will follow a so-called open loop
profile based on the previous operating cycle temperature sensed by
sensor 43 and the position of the valve 36 at compressor shutdown.
Thus, a feedback control algorithm is gradually phased in over time
as indicated by the "weight" column. Moreover, as indicated by the
table of FIG. 7, a startup profile in accordance with the invention
includes parameters of relative position and valve control due to
the fixed profile, or not. Also, the "weight" at time equal zero
must be one hundred and the "weight" must be zero by the end of the
one hundred eighty second startup period.
[0040] A preferred embodiment of an expansion valve, such as
expansion valve 36, 36a and 36b, may be one commercially available,
such as a model CAM from Fujikoki or a model UKV from Saginomiya.
The control unit or controller 34, 34a or 34c is capable of
modulating the stepper motor type expansion valve 36, 36a or 36b in
one of at least three operating modes where the control unit and
the expansion valve and associated sensors are installed in a
so-called indoor unit, such as a so-called air handler or encased
heat exchanger, including the evaporator 12. Alternatively, for a
system operating in a heating mode, the controller or control unit
and an expansion valve may be installed in an outdoor unit, such as
illustrated in FIGS. 2 and 3. For operation in both heating and
cooling mode, the expansion valve and control unit would be
installed between the indoor unit and outdoor unit, typically, with
pressure and temperature sensors installed on the common compressor
suction line(s), such as conduit 30.
[0041] Referring to FIG. 8, there is illustrated a more detailed
diagram of a control unit or controller for operating the motor
controlled expansion valves of the present invention. In a
conventional application for residential or commercial air
conditioning apparatus provided with 24 volt AC electrical power,
the control unit 34, 34a or 34c may be installed as a stand-alone
device capable of sensing standard 24 volt air conditioning
apparatus control signals such as by monitoring a call for startup
of a compressor at a Y1 or Y2 line or conductor, plus a signal to
the switchover or reversing valve provided by conductor O for
establishing the mode of operation and the compressor status. The
designations Y1, Y2 and O are in keeping with HVAC equipment code
standards prescribed by the American National Standards Institute.
Based on compressor status, the control unit 34, 34a or 34c will
modulate the position of the expansion valve to control superheat.
Alternatively, the control unit 34, 34a and 34c may be installed as
a subordinate to a master controller enabling communication between
the controller and the master controller.
[0042] The control unit illustrated schematically in FIG. 8 is
designated by the numeral 34d, for convenience and corresponds to
control units 34, 34a and 34c. Control unit 34d includes circuitry
for receiving a twenty-four volt AC power supply via conductors 110
and 112, and signals via conductor 114 and conductor 116
corresponding to the so-called Y1 and Y2 signals and a signal
indicating the position of a switchover or reversing valve via
conductor 118, otherwise known as the valve control signal O
together with a serial communication conductor 120. Control unit
34d is operable to output a signal via conductor 122 to control the
operation of a compressor such as the compressor 26. Control unit
34d is suitably operably connected to expansion valve 36, 36a or
36b and is operable to receive input signals from a pressure
transducer such as transducer or sensor 40a and temperature sensor
40b, as well as a temperature sensor 43 or 38. A series of DIP
switches 124, jumpers or other means may be provided to configure a
microprocessor 34e of the controller or control unit 34d with
respect to such parameters as refrigerant type, size of the motor
operated expansion valve, low stage capacity for a multi-stage
system, high stage capacity, and applications such as cooling mode,
heating mode or dual mode, for example. Output signals are, of
course, available for signaling the compressor via conductor 122,
the expansion valve, as indicated, and, preferably, a light signal,
such as a LED indicator 126, for use in diagnostic indications. The
sensors 40b and 43 may be of a type commercially available, such as
of the thermistor type, and the pressure sensor or transducer 40a
may be of a type commercially available and suitable for use with
refrigerants R22 and R410A, for example.
[0043] Referring briefly to FIG. 9, there is illustrated a diagram
of the change in the evaporator temperature to reach a
predetermined amount of superheat, such as 10.degree. F., versus
the current superheat condition as measured by the sensors
connected to the control unit. Accordingly, the control unit 34,
34a, 34b, 34c or 34d may be programmed to compare current superheat
conditions and using data represented by the line 125 in FIG. 9,
adjust the position of the motor operated expansion valve to
maintain a predetermined amount of superheat, such as the
referenced 10.degree. F. However, to further simplify the method of
the invention, the change in evaporator temperature required to
reach 10.degree. F. superheat may be set to a constant value.
[0044] The construction and operation of the various embodiments of
the invention described hereinabove, are believed to be within the
purview of one skilled in the art based on the foregoing
description. Commercially available components may be used to
construct the various embodiments of the apparatus described herein
and the control units 34, 34a, 34b, 34c, and 34d may also be
constructed utilizing control circuitry including programmable
microcontroller or microprocessor type devices known to those
skilled in the art. Although preferred embodiments of the invention
have been described in detail, those skilled in the art will also
recognize that various substitutions and modifications may be made
without departing from the scope and spirit of the appended
claims.
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